Specifically, they were proposing reductions to the payroll mobility tax, which was established in 2009 to help shore up the authority’s teetering finances by levying a 34-cent tax on every $100 of payroll for employees in the 12 counties served by the M.T.A.

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It is not popular in the suburbs.

“Thankfully, with Governor Cuomo’s cooperation, we recently eliminated this tax for employers with payrolls of less than $1.25 million,” wrote Martins a couple of days later in a column on Patch.com.

Martins was referring to the grand budget compromise hammered out by Cuomo and legislative leaders in December, in which the governor gave Senate Republicans a payroll mobility tax cut in exchange for their support of a tax hike on high-income earners. The move was estimated to cut about $300 million a year from the M.T.A.’s operating budget, which the governor and legislature promised to reimburse from the state’s general fund.

In this year's proposed budget, the governor kept his promise. But as Gene Russianoff, staff attorney for the Straphangers Campaign, points out, whether Cuomo and his successors will continue to make good on their promise isn't clear. And that is precisely the argument against further cuts to a dedicated tax in favor of discrete budget allocations that are by definition subject to the changing whims of elected officials.

“That’s got to keep happening in future years," said Russianoff. "[The M.T.A.] will be under tremendous pressure if they don’t fund that $310 million on an annual basis in 2013, 2014, 2015. And that’s before you even get to these bills.”

By "these bills," Russianoff was referring to a Martins-and Zeldin-sponsored proposal that would, “exempt all counties, towns, cities, villages and other political subdivisions outside of New York city from paying the metropolitan commuter transportation mobility tax," and another one, sponsored by Martin, that would exempt libraries. The former, according to the bill’s sponsors, would cut some $30 million from the M.T.A.’s annual budget. (The $56 million number mentioned in the text of the bill was a miscalculation, according to Martins' spokesman, Joe Rizza.) The latter bill, according to Rizza, would cut $1.6 million.

“Property taxpayers paying for village, town and county services should not have their hard-earned tax dollars diverted to subsidize the M.T.A. through this payroll tax," said Martins at the press conference.

Of course his equation doesn't factor in the role that the Long Island Railroad, part of the M.T.A., plays in supporting Long Island's economy. Tax-paying Mineola residents commute to jobs in New York City using the infrastructure that Martins and Zeldin seek to defund.

And Long Island commuters are already more subsidized than most: In 2012, LIRR fares are expected to make up 45 percent of the train lines’ operating costs, according to NYPIRG, the umbrella group that includes the Straphangers Campaign. By contrast, subway and bus riders pay 56 percent of the system’s operating costs, and Metro North riders pay 57 percent. The rest comes from other revenue sources, like the M.T.A. payroll mobility tax.

The bills, on their own, are unlikely to find enough support to pass in the Democratic-controlled Assembly. But no one knows what will happen the next time the opportunity for a grand bargain comes around.

“I take them seriously," Russianoff said. "You’ve got to, because they were successful before, to the tune of $310 million.”